Critical illness insurance provides a lump sum payment if the policyholder is diagnosed with a specified critical illness. It can help cover costs if the person is unable to work due to a serious illness like cancer, stroke, or heart attack. The payment is made as long as the policyholder survives more than a month after diagnosis. Policies vary by insurer but typically cover around 30 illnesses and can be purchased through an insurer or advisor. The cost of coverage depends on factors like age, health, smoking status, and amount of coverage. Claims require medical evidence and meeting the insurer's criteria for the illness.